Re weather balloons:
Depends on the type of balloon being released and general conditions but on an average day an 800gm balloon with radiosonde attached would obtain 34-37km, 350gm balloon also with radiosonde attached approx 26-28km and a 100gm balloon wind-only flight around 17-20km.
Size wise, the 350 and especially 800gm balloons at burst are around the size of a small house at burst.
Hope this helps